1. Field of the Invention
This invention relates to insulation structures and methods for the insulation of interior surfaces of annular ducts.
2. Description of the Background Art
Current application of low density thermal and/or acoustic insulation to the interior surface of annular duct systems typically requires a three component structure: (1) annular duct shell, (2) low density fiber, such as fiberglass, and (3) annular (perforated or solid) insulated retaining insert. (see FIG. 5). The purpose of the retaining insert is to hold the insulation material against the interior wall of the annular duct. Fiberglass insulation materials do not have sufficient structural integrity to maintain an unaided annular shape, and cannot be installed in annular ducts without the use of strong adhesives, mechanical fasteners and/or annular retaining inserts. The use of limited open time contact adhesives is prohibitive due to health hazards and surface area application limits associated with short setup time. The installation of metal retaining inserts is costly, requires special safety equipment and practices, reduces the NRC (noise reduction coefficient) of the installed insulation, and increases the installed weight of the duct sections by ⅓ or greater.
Prior attempts to replace fiberglass with closed cell elastomer and polymer foams have all resulted in failure. Closed cell foams are extremely difficult to install between the duct shell and insulation retaining insert due to the magnitude of the resulting insertion force.
There remains a need in the art for improved insulation structures and methods for the insulation of interior surfaces of annular ducts.